UN minority rights expert Rita Izsak urged the world community from Geneva on Tuesday that "all possible measures" must be taken to rescue Yazidis in Iraq. Up to 30,000 members of the minority group are still trapped on Sinjar Mountain.
Izsak said in a joint statement with fellow monitors that the Iraqi civilians were in "extreme peril" and needed to be escorted to safety.
Christof Heyns, UN expert on arbitrary executions, said "Islamic State" fighters had presented non-Muslims with a "convert or die" option.
Refugee rights monitor, Chaloka Beyani, told the world: "We are witnessing a tragedy of huge proportions unfolding, in which thousands of people are at immediate risk of death by violence or by hunger and thirst."
30,000 still on Sinjar mountain
UN refugee agency spokesman Adrian Edwards said while some 35,000 people had managed to flee the barren range - looping via Syria into Iraqi Kurdish regions - a further 20,000 to 30,000 people remained on Sinjar Mountain.
Edwards applauded local Iraqis - mainly Kurds - for taking in refugees driven from their homes by recent IS advances, including Yazidis, Christians and Turkmen minorities.
Those arriving were "exhausted and dehydrated," Edwards said. Many had suffered sun or heat stroke in temperaturs reaching 45 degrees Celsius (113 degrees Fahrenheit).
World Health Organization (WHO) spokesman Paul Garwood said two medical teams had reached the mountain. Supplies had been sent by helicopter.
In recent days, the US, Britain and France have also air dropped water, food and solar lamps to refugees on the range. The US has staged air strikes against IS fighters.
Women 'kidnapped, some 'executed'
From Geneva, UN special rapporteur on violence against women, Rashida Manjoo, said the UN had "unverified reports that strongly suggest that hundreds of women and children have been kidnapped.
"Many of the teenagers have been sexually assaulted, and women have been assigned or sold to IS fighters as 'malak yamiin' or slaves," Manjoo said.
Manjoo added that the UN also had "reports of women being executed."
Religious rights monitor Heiner Beilefeldt said freedom of faith in Iraqi areas held by the IS was being "denied in the most gross and systematic way possible, through the attempted extermination of religious minorities."
More than a million displaced
Across Iraq are more than 1.2 million internally displaced people, according to UN counts. These include 700,000 in the semi-autonomous northern Kurdish region.
Another 10,000 to 15,000 Yazidis have opted to flee to war-torn Syria, said the UNHCR.
Since June, IS militants have expanded control from eastern Syria, seizing tracts of adjacent northwestern Iraq and declaring a mediaeval-style caliphate in the oil-rich swathes it holds.
Helicopter crash on Sinjar
An Iraqi helicopter delivering aid to those stranded crashed Tuesday on Sinjar, killing its pilot and injuring parliamentarian Vian Dakheel.
She and other injured were evacuated to hospital in the nearby Kurdish region.
Dakheel's emotional appeal in the Iraqi parliament last week put the focus on the Yazidis' plight.
ipj/sb (dpa, AFP)